Sang-Hee Ko Park

42.3: Transparent ZnO Thin Film Transistor for the Application of High Aperture Ratio Bottom Emission AM-OLED Display

We have fabricated 2.5″ QCIF+ bottom emission AM-OLED with aperture ratio of 59.6% using fully transparent ZnO-TFT array and highly conductive oxide/metal/oxide electrode for the first time. The bias stability of ZnO TFT was improved by optimizing ZnO deposition and first gate insulator process. Plasma free process for the gate insulator makes ZnO TFT very stable under electrical bias stress. The Vth shift was less than 0.3V after VDS=25 V and VGS=15 V application for 60 hours. Transparent ZnO TFT characteristics did not change noticeably under irradiation of visible light.

21.2: Al and Sn-Doped Zinc Indium Oxide Thin Film Transistors for AMOLED Back-Plane

We have fabricated the transparent bottom gate TFTs using Al and Sn-doped zinc indium oxide (AT-ZIO) as an active layer. The AT-ZIO active layer was deposited by RF magnetron sputtering at room temperature, and AT-ZIO TFT showed a field effect mobility of 15.6 cm2/Vs even before annealing. The mobility increased with increasing In2O3 content and post-annealing temperature. The AT-ZIO TFT exhibited afield effect mobility of 33 cm2/Vs, a sub-threshold swing of 0.08 V/dec, and an on/off current ratio of more than 109 after Al2O3 passivation and post-annealing. We have fabricated AMOLED panels with the bottom gate AT-ZIO TFT back-plane successfully.

Photon-accelerated negative bias instability involving subgap states creation in amorphous In–Ga–Zn–O thin film transistor

We investigated the visible photon accelerated negative bias instability (NBI) in amorphous In–Ga–Zn–O (a-IGZO) thin film transistor (TFT). As reported in previous works, the rigid shift in transfer curves with insignificant changes in field-effect mobility and subthreshold swing was observed. On the other hand, there is substantial change in capacitance-voltage characteristics caused by created subgap states. The suggested nature of created states is the ionized oxygen vacancy (VO2+) by the combination of visible light and negative bias. The generated VO2+ states enhance the NBI under illumination as increased deep hole trapping centers. Furthermore, the photoexcitation of VO to stable VO2+ yields excess free carriers in conduction band. The increased carrier density also enhances the negative shift in turn-on voltage of a-IGZO TFT.

Transparent p-type SnOx thin film transistors produced by reactive rf magnetron sputtering followed by low temperature annealing

P-type thin-film transistors (TFTs) using room temperature sputtered SnOx (x<2) as a transparent oxide semiconductor have been produced. The SnOx films show p-type conduction presenting a polycrystalline structure composed with a mixture of tetragonal β-Sn and α-SnOx phases, after annealing at 200 °C. These films exhibit a hole carrier concentration in the range of ≈1016–1018 cm−3; electrical resistivity between 101–102 Ω cm; Hall mobility around 4.8 cm2/V s; optical band gap of 2.8 eV; and average transmittance ≈85% (400 to 2000 nm). The bottom gate p-type SnOx TFTs present a field-effect mobility above 1 cm2/V s and an ON/OFF modulation ratio of 103.

Thin-film transistors based on p-type Cu2O thin films produced at room temperature

Copper oxide (Cu2O) thin films were used to produce bottom gate p-type transparent thin-film transistors (TFTs). Cu2O was deposited by reactive rf magnetron sputtering at room temperature and the films exhibit a polycrystalline structure with a strongest orientation along (111) plane. The TFTs exhibit improved electrical performance such as a field-effect mobility of 3.9 cm2/V s and an on/off ratio of 2×102.

Transparent Al–Zn–Sn–O thin film transistors prepared at low temperature

We have fabricated transparent bottom gate thin film transistors (TFTs) using Al-doped zinc tin oxide (AZTO) as active layers. The AZTO active layer was deposited by rf magnetron sputtering at room temperature. The AZTO TFT showed good TFT performance without postannealing. The field effect mobility and the subthreshold swing were improved by postannealing below 180 °C. The AZTO TFT exhibited a field effect mobility (μFET) of 10.1 cm2/V s, a turn-on voltage (Von) of 0.4 V, a subthreshold swing (S/S) of 0.6 V/decade, and an on/off ratio (Ion/Ioff) of 109.

Ultrathin Film Encapsulation of an OLED by ALD

Fabrication of barrier layers on a PES film and an organic light emitting diode (OLED) based on a glass substrate by atomic layer deposition (ALD) have been carried out. Deposition of 30 nm of film on both sides of PES film at 90°C gave film MOCON value of The passivation performance of the double layer consisting of deposited by plasma-enhanced chemical vapor deposition and by ALD on the OLED has been investigated using the OLED based on a glass substrate. Preliminary life time of two pairs of double layer coated OLED to 65% of initial luminance was 600 h at the initial luminance of

Comparative Study on Light-Induced Bias Stress Instability of IGZO Transistors With

This letter examines the effect of the gate dielectric material on the light-induced bias-temperature instability of an In-Ga-Zn-O (IGZO) thin-film transistor (TFT). After applying positive and negative bias stresses, the SiNx-gated TFT exhibited inferior stability to the SiO2-gated TFT, which was explained by the charge trapping mechanism. However, light illumination under a negative bias stress accelerated the negative displacement of the threshold voltage (Vth) of the SiNx-gated IGZO TFT compared to that of the SiO2-gated TFT. This was attributed to the injection of photocreated hole carriers into the underlying gate dielectric bulk region as well as the hole trapping at the gate/channel interface.

\hbox{SiN}_{x}

This study examined the impact of the passivation layer on the light-enhanced bias instability of Al–Sn–Zn–In–O (AT–ZIO) thin film transistors. The suitably passivated device exhibited only a threshold voltage (Vth) shift of 0.72 V under light-illuminated negative-thermal stress conditions, whereas the device without a passivation layer suffered from a huge negative Vth shift of >11.5 V under identical conditions. The photocreated hole trapping model could not itself explain this behavior. Instead, the light-enhanced Vth instability of the unpassivated device would result mainly from the photodesorption of adsorbed oxygen ions after exposing the AT–ZIO back-surface in an ambient atmosphere.

and

Transparent ZnO thin film transistor (TFT) array of 176 X 144 (106 dpi) was fabricated on glass substrate. The V th of the TFT with inverted coplanar structure is about 0.8 V and the mobility is 1.13 cm 2 /V s. The active layer (ZnO), gate insulator (Al 2 O 3 ), and source-drain electrode (ZnO:Al) were deposited by atomic layer deposition. We also compared the performance of TFTs fabricated by lift-off and wet-etching process as the patterning processes of ZnO layer. The carrier density of the ZnO layer was carefully adjusted to reduce off-current of TFT. Good contact with small contact resistance was formed between the active layer and the source-drain electrode.